Dielectric ceramic and laminated ceramic capacitor

A dielectric ceramic which is capable of achieving a laminated ceramic capacitor with high reliability, in particular, favorable lifetime characteristics in a load test, even when a dielectric ceramic layer is reduced in thickness contains one of (Ba,R)(Ti,Mn)O3 and (Ba,Ca,R)(Ti,Mn)O3 (R being La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and/or Y) as a main component, and M (M being Fe, Co, V, W, Cr, Mo, Cu, Al, and/or Mg) and Si as accessory components. The area of a region in which M is present is 10% or less on average of a cross section of each main component grain.

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Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dielectric ceramic and a laminated ceramic capacitor, and more particularly, relates to a dielectric ceramic suitable for use in a thin-layer high-capacity laminated ceramic capacitor, and a laminated ceramic capacitor made using the dielectric ceramic.

2. Description of the Related Art

As one of effective means for satisfying the needs for size reduction and higher capacity of laminated ceramic capacitors, dielectric ceramic layers provided in laminated ceramic capacitors are sometimes reduced in thickness. However, the electric field intensity per dielectric ceramic layer is increased as the dielectric ceramic layers become thinner and thinner. Therefore, a higher reliability, in particular, higher lifetime characteristics in a load test is required for the dielectric ceramic used.

BaTiO3 based dielectric ceramics are often used as dielectric ceramics constituting dielectric ceramic layers of laminated ceramic capacitors. In order to improve the reliability and various electric properties of the BaTiO3 based dielectric ceramics, elements such as rare-earth elements and Mn may be added as accessory components.

For example, Japanese Patent Application Laid-Open No. 10-330160 (Patent Document 1) discloses, for the purpose of improving the dielectric breakdown voltage, a dielectric ceramic which has a core-shell structure and contains ABO3 (A always contains Ba, and may further contain at least one of Ca and Sr, while B always contains Ti, and may further contain at least one of Zr, Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm, and Lu) as its main component, and in the dielectric ceramic, at least one of Mn, V, Cr, Co, Ni, Fr, Nb, Mo, Ta, and W is substantially homogeneously distributed through the grains. In addition, Patent Document 1 discloses an example in which Mg is used as a shell component and is distributed only in the shell portion, but not in the core.

However, the reliability of the dielectric ceramic described in Patent Document 1 mentioned, and in particular, the lifetime characteristics in a load test, may be insufficient as the dielectric ceramic layers are further reduced in thickness, and therefore, further improvements have been desired.

SUMMARY OF THE INVENTION

Thus, some of the objects of the present invention is to provide a dielectric ceramic which is capable of achieving high reliability even when a dielectric ceramic layer is reduced in thickness, and provide a laminated ceramic capacitor composed with the use of the dielectric ceramic.

The present invention includes a dielectric ceramic containing one of (Ba,R)(Ti,Mn)O3 and (Ba,Ca,R)(Ti,Mn)O3 (where R is at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) as a main component; and M (where M is at least one of Fe, Co, V, W, Cr, Mo, Cu, Al, and Mg) and Si as accessory components. In order to solve the above-mentioned technical problem, the dielectric ceramic of the invention has the feature that the area of a region in which M is present is 10% or less on average on a cross section of each main component grain.

In the dielectric ceramic according to the present invention, the Mn content is preferably 0.01 to 1 mol % with respect to all of (Ti,Mn) sites.

The R content is preferably 0.01 to 2 mol % with respect to all of (Ba,R) sites or (Ba,Ca,R) sites.

The Ca content is preferably 15 mol % or less with respect to all of (Ba,Ca,R) sites.

The present invention is also directed to a laminated ceramic capacitor including a capacitor main body including a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along specific interfaces between the dielectric ceramic layers; and a plurality of external electrodes formed in positions different from each other on an external surface of the capacitor main body and electrically connected to specific ones of the internal electrodes.

The laminated ceramic capacitor according to the invention has a feature that the dielectric ceramic layers are composed of the dielectric ceramic according to the invention.

In the dielectric ceramic according to the invention, Mn is present homogeneously as a solid solution in the main component grains, thereby improving the insulating property in the main component grains. In addition, R is also present homogeneously as a solid solution in the main component grains, thereby improving the insulating property in the main component grains.

The solid solution region with the M component as an accessory component therein is 10% or less, and local grain growth can be thus suppressed on firing. Therefore, when a laminated ceramic capacitor is constructed using the dielectric ceramic according to the invention, the fired dielectric ceramic layers can be made smoother. This is advantageous for reduction in the thickness of the laminated ceramic capacitor, and a high reliability, in particular, favorable lifetime characteristics in a load test can be maintained even in the thinned laminated ceramic capacitor.

No local grain growth is caused when Mn and R are present homogeneously as a solid solution in the main component grains. However, it is believed that the local grain growth is likely to be caused when Mn and R are present homogeneously as a solid solution in the main component grains, and M is further present at a constant rate or more in the main component grains. In this regard, when the amount of the solid solution region with the M component therein is 10% or less as described above, it is expected that local grain growth may be suppressed.

In the dielectric ceramic, when the main component is (Ba,Ca,R)(Ti,Mn)O3, that is, when Ca is present as a solid solution at Ba sites, the action of suppressing the local grain growth is further enhanced, and the reliability is further improved.

In the dielectric ceramic, when the Mn content ratio is 0.01 to 1 mol % with respect to all of (Ti,Mn) sites, the lifetime characteristics can be further improved.

In addition, when the R content in the dielectric ceramic is 0.01 to 2 mol % with respect to all of (Ba,R) sites or (Ba,Ca,R) sites, the lifetime characteristics can be further improved.

In addition, when the Ca content in the dielectric ceramic is 15 mol % or less with respect to all of (Ba,Ca,R) sites, the lifetime characteristics can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically illustrating a laminated ceramic capacitor 1 formed with the use of a dielectric ceramic according to the invention; and

FIG. 2 is a cross sectional view schematically illustrating main component grains 11 of a dielectric ceramic according to the invention.

 DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a laminated ceramic capacitor 1 with a dielectric ceramic according to the invention applied will be described first.

The laminated ceramic capacitor 1 includes a capacitor main body 5 composed of a plurality of stacked dielectric ceramic layers 2 and of a plurality of internal electrodes 3 and 4 formed along specific interfaces between the dielectric ceramic layers 2. The internal electrodes 3 and 4 contain, for example, Ni as their main component.

First and second external electrodes 6 and 7 are formed in positions different from each other on an external surface of the capacitor main body 5. The external electrodes 6 and 7 contain, for example, Ag or Cu as their main component. In the laminated ceramic capacitor 1 shown in FIG. 1, the first and second external electrodes 6 and 7 are formed on end surfaces of the capacitor main body 5 opposed to each other. As for the internal electrodes 3 and 4, the plurality of internal electrodes 3 and the plurality of internal electrodes 4 are electrically connected respectively to the first external electrode 6 and the second external electrode 7, and the first and second internal electrodes 3 and 4 are arranged alternately with respect to the stacking direction.

It is to be noted that the laminated ceramic capacitor 1 may be a two-terminal laminated ceramic capacitor provided with the two external electrodes 6 and 7, or may be a multi-terminal laminated ceramic capacitor provided with a number of external electrodes.

In this laminated ceramic capacitor 1, the dielectric ceramic layers 2 are composed of a dielectric ceramic containing a (Ba,R)(Ti,Mn)O3 or (Ba,Ca,R)(Ti,Mn)O3 (R being at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) as its main component, and M (where M is at least one of Fe, Co, V, W, Cr, Mo, Cu, Al, and Mg) and Si as accessory components.

FIG. 2 shows a cross sectional view of main component grains 11 of the dielectric ceramic schematically. Referring to FIG. 2, Mn and R are present homogeneously as a solid solution in most regions of the main component grains 11 as described above. On the other hand, M is not present as a solid solution in the main component grains 11. More specifically, the region in which M is present (hereinafter, referred to as an “M region”) 12 is formed on the surface portion of the main component grains 11. However, the M region 12 is not present so as to form a thin shell in a concentric fashion with the main component grains 11. Therefore, the main component grains 11 do not have a core-shell structure, unlike the case of the dielectric ceramic described in Patent Document 1 mentioned above.

The dielectric ceramic constituting the dielectric ceramic layers 2 has the feature that the amount of the area of the M region 12 on a cross section of each main component grain 11 is 10% or less on average.

In the dielectric ceramic, Mn and R are present homogeneously as a solid solution in the main component grains, thereby allowing the insulating property of the main component grains 11 to be improved. In this case, the amount of the area of the M region 12 on a cross section of the main component grain 11 is only 10% or less, thus allowing local grain growth to be suppressed on firing. Therefore, even when the laminated ceramic capacitor is reduced in thickness, a high reliability can be achieved, and in particular, favorable lifetime characteristics in a load test can be achieved.

When the content of Mn is 0.01 to 1 mol % with respect to all of (Ti,Mn) sites, the lifetime characteristic can be further improved.

When the content of R is 0.01 to 2 mol % with respect to all of (Ba,R) sites or (Ba,Ca,R) sites, the lifetime characteristic can be further improved.

In addition, when the dielectric ceramic contains (Ba,Ca,R)(Ti,Mn)O3 as its main component, that is, when Ca is present as a solid solution at Ba sites, the action of suppressing the local grain growth is further enhanced, and the reliability is further improved. When the Ca content ratio is 15 mol % or less with respect to all of (Ba,Ca,R) sites, the lifetime characteristic can be further improved.

In order to produce a raw material for the dielectric ceramic, a (Ba,R)(Ti,Mn)O3 or (Ba,Ca,R)(Ti,Mn)O3 based main component powder is first produced. For example, a solid-phase synthesis method is applied in such a way that compound powders containing constituent elements for the main component, such as powders of oxides, carbides, chlorides, and metallic organic compounds, are mixed at predetermined ratios and calcined. In this case, the grain diameters of the obtained main component powder are controlled by controlling, for example, the calcination temperature. It is to be noted that a hydrothermal synthesis method or a hydrolysis method may be applied instead of the solid-phase synthesis method.

Compound powders containing each of M and Si as accessory components, such as powders of oxides, carbides, chlorides, and metallic organic compounds, are prepared. Then, these accessory component powders are mixed with the main component powder at predetermined ratios, thereby giving a raw material powder for the dielectric ceramic.

In order to manufacture the laminated ceramic capacitor 1, the dielectric ceramic raw material powder obtained as described above is used to produce a ceramic slurry, ceramic green sheets are formed from the ceramic slurry, a conductive paste is applied to the sheets (to become the internal electrodes), and the resulting multiple ceramic green sheets are stacked, thereby giving a raw laminate to serve as the capacitor main body 5, and the step of firing the raw laminate is carried out. In this step of firing the raw laminate, the dielectric ceramic raw material powder blended as described above is fired, thereby giving the dielectric ceramic layers 2 composed of the sintered dielectric ceramic.

When, for example, the dielectric ceramic raw material powder, a binder, and an organic solvent are mixed with media balls in a ball mill in order to produce the ceramic slurry, the solid solution region with M present therein in the main component grains of the sintered dielectric ceramic, that is, the area of the M region, can be controlled by adjusting the diameters of the balls used in this step. Of course, methods other than the control of the ball diameters, for example, a method of adjusting the mixing time may be applied in order to control the extent ratio of the area of the M region.

Experimental examples carried out in accordance with the invention will be described below.

Experimental Example 1

In Experimental Example 1, dielectric ceramics containing (Ba,R)(Ti,Mn)O3 as a main component and having varied areas of the M region were evaluated.

(A) Production of Ceramic Raw Material

First, respective powders of fine BaCO3, TiO2, Y2O3, and MnCO3 were prepared as starting materials for the main component, weighed to provide (Ba0.99Y0.01)(Ti0.995Mn0.005)O3, and mixed with water as a medium in a ball mill for 8 hours. Then, evaporative drying was carried out, and calcination was carried out at a temperature of 1100° C. for 2 hours, thereby giving a main component powder.

Next, respective powders of V2O5 and SiO2 to serve as accessory components were prepared, and weighed so that 0.25 parts by mol of V as M and 1.5 parts by mol of Si were contained with respect to 100 parts by mol of the main component were present and blended with the main component powder, followed by mixing with water as a medium in a ball mill for 24 hours. Then, evaporative drying was carried out, thereby giving a dielectric ceramic raw material powder.

(B) Production of Laminated Ceramic Capacitor

To the ceramic raw material powder, a polyvinyl butyral based binder and ethanol were added, followed by mixing in a wet manner in a ball mill for 16 hours to produce a ceramic slurry. In this step of mixing in a wet manner in the ball mill, the balls used were changed to have diameters of 2 mm, 1.5 mm, 1 mm, 0.8 mm, 0.6 mm, 0.5 mm, and 0.3 mm, respectively, for samples 101, 102, 103, 104, 105, 106, and 107, thereby changing the amount of the area of the region with M (=V) therein in main component grains of a sintered dielectric ceramic obtained in a subsequent firing step, that is, the “Ratio of Area of M region” as shown in Table 1.

Next, this ceramic slurry was formed into the shape of a sheet by a lip method, thereby giving ceramic green sheets.

Next, a conductive paste mainly containing Ni was screen-printed on the ceramic green sheets to form conductive paste films to serve as internal electrodes.

Next, the multiple ceramic green sheets with the conductive paste films formed were stacked so that the drawn ends of the conductive paste films are alternately arranged, thereby giving a raw laminate to serve as a capacitor main body.

Next, the raw laminate was heated to a temperature of 300° C. in an N2 atmosphere to burn off the binder, and then fired at a temperature of 1200° C. for 2 hours in a reducing atmosphere composed of an H2—N2—H2O gas with an oxygen partial pressure of 10−10 MPa, thereby giving a sintered capacitor main body.

Next, a Cu paste containing a B2O3—Li2O—SiO2—BaO based glass frit was applied on the opposite end surfaces of the sintered capacitor main body, and fired at a temperature of 800° C. in an N2 atmosphere to form external electrodes electrically connected to the internal electrodes, thereby giving a laminated ceramic capacitor as a sample.

The thus obtained laminated ceramic capacitors had outer dimensions of 2.0 mm in length, 1.2 mm in width, and 1.0 mm in thickness, and the dielectric ceramic layers interposed between the internal electrodes had a thickness of 1.0 μm. The number of the effective dielectric ceramic layers was 100, whereas the area of the internal electrode opposed per ceramic layer was 1.4 mm2.

(C) Structural Analysis and Characterization of Ceramic

The ceramic structure of the laminated ceramic capacitors obtained was observed and analyzed on a cross section of the dielectric ceramic layer. In the observation and analysis, an EDX element mapping analysis in accordance with a STEM mode was carried out in a field of view including around 20 grains to calculate the amount of the solid solution area for the V (=M) component as the subsequently added accessory component in the grains, and obtain the average value for the ratio of the solid solution areas in the field of view. The results are shown in the column of “Ratio of Area of M region” in Table 1. It is to be noted that in the mapping analysis, the probe diameter was 2 nm, whereas the accelerating voltage was 200 kV.

In addition, a high temperature load life test was carried out for the laminated ceramic capacitors obtained. In the high temperature load life test, a direct current voltage of 12 V (with an electric field intensity of 12 kV/mm) was applied to 100 samples at a temperature of 125° C., and a sample was regarded as defective when the insulation resistance value was deceased to 100 kΩ or less before a lapse of 1000 hours or 2000 hours, thereby giving the number of defectives. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 1.

TABLE 1 Number of Defectives in High Sample Ratio of Area Temperature Load Life Test Number of M region 1000 hours 2000 hours 101 0 0/100 0/100 102 5 0/100 0/100 103 10 0/100 0/100 104 11 1/100 2/100 105 15 3/100 4/100 106 20 5/100 6/100 107 50 7/100 9/100

As can be seen from Table 1, samples 101 to 103 had a “Ratio of Area of M region” of 10% or less, no detective was realized in the high temperature load life test, not only after a lapse of 1000 hours but also after a lapse of 2000 hours.

On the other hand, samples 104 to 107 had a “Ratio of Area of M region” over 10%, and defective(s) were present after a lapse of 1000 hours in the high temperature load life test.

It is determined from these results that favorable reliability can be obtained when the main component is (Ba,R)(Ti,Mn)O3 and when the “Ratio of Area of M region” is 10% or less.

Experimental Example 2

In Experimental Example 2, a dielectric ceramic was evaluated containing (Ba,R)(Ti,Mn)O3 as a main component as in the case of Experimental Example 1 and having the Mn content and R content varied.

(A) Production of Ceramic Raw Material

A dielectric ceramic raw material powder was obtained in the same way as in the case of Experimental Example 1, expect that while using Dy as R, the composition of (Ba1−x/100DYx/100)(Ti1−y/100Mny/100)O3 as a main component powder was adjusted so that the content x of Dy as R at (Ba,R) sites and the content y of Mn at (Ti,Mn) sites, respectively, had values shown in the columns “x” and “y” in Table 2.

(B) Production of Laminated Ceramic Capacitor

The dielectric ceramic raw material powder was used to manufacture laminated ceramic capacitors in the same way as in the case of Experimental Example 1. It is to be noted that in the step of mixing in a wet manner in a ball mill, balls 1.5 mm in diameter were used to mix the powders for 16 hours, as in the case of sample 102 in Experimental Example 1.

(C) Structural Analysis and Characterization of Ceramic

The ceramic structure analysis carried out in the same way as in the case of Experimental Example 1 resulted in a “Ratio of Area of M region” of around 3.5% for any of samples 201 to 210.

In addition, the high temperature load life test was carried out in the same way as in the case of Experimental Example 1. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 2.

TABLE 2 Number of Defectives in High Sample Temperature Load Life Test No. x y 1000 hours 2000 hours 201 1.50 0.50 0/100 0/100 202 0.20 0.70 0/100 0/100 203 1.90 0.60 0/100 0/100 204 0.01 1.00 0/100 0/100 205 2.00 1.20 0/100 0/100 206 2.10 0.50 0/100 1/100 207 1.50 0.01 0/100 0/100 208 0.90 1.00 0/100 0/100 209 0.60 1.10 0/100 2/100 210 2.40 1.30 0/100 3/100

As can be seen from Table 2, samples 201 to 205, 207, and 208 had a content “x” of Dy as R in the range of 0.01 to 2 and a content “y” of Mn in the range of 0.01 to 1.0, and no detectives were realized in the high temperature load life test, not only after a lapse of 1000 hours but also after a lapse of 2000 hours.

On the other hand, samples 206, 209, and 210 had a content “x” of Dy as R outside the range of 0.01 to 2 or the content “y” of Mn was outside the range of 0.01 to 1.0, and while no defective was formed after a lapse of 1000 hours, defective(s) were formed after a lapse of 2000 hours in the high temperature load life test.

It is determined from these results that higher reliability can be obtained when the R content “x” falls within the range of 0.01 to 2 and when the Mn content “y” falls within the range of 0.01 to 1.0.

Experimental Example 3

In Experimental Example 3, the influences of the impurities were evaluated while using (Ba,R)(Ti,Mn)O3 as a main component in the same way as in the case of Experimental Example 1.

In the process of manufacturing a laminated ceramic capacitor such as the production of the raw material, there is a possibility that Sr, Zr, Hf, Zn, Na, Ag, Pd, Ni, and the like, are present as impurities in a dielectric ceramic, and present in crystal grains and at crystal grain boundaries between the crystal grains. In addition, for example, when firing a laminated ceramic capacitor, there is a possibility that a component of internal electrodes is diffused and present in crystal grains of the dielectric ceramic and at crystal grain boundaries between the crystal grains. Experimental Example 3 is intended to evaluate the influences of these impurities.

(A) Production of Ceramic Raw Material

A dielectric ceramic raw material powder was obtained in the same way as in the case of Experimental Example 1, expect that amounts of impurity components shown in Table 3 were added to 100 parts by mol of the dielectric ceramic raw material obtained in Experimental Example 1, so as to provide the content shown.

(B) Production of Laminated Ceramic Capacitor

The dielectric ceramic raw material powder was used to manufacture laminated ceramic capacitors in the same way as in the case of Experimental Example 1. It is to be noted that in the step of mixing in a wet manner in a ball mill, balls 1.5 mm in diameter were used to mix the powders for 16 hours, as in the case of sample 102 in Experimental Example 1.

(C) Structural Analysis and Characterization of Ceramic

The ceramic structure analysis carried out in the same way as in the case of Experimental Example 1 resulted in the “Ratio of Area of M region” of around 3.5% for any of samples 301 to 310.

In addition, the high temperature load life test was carried out in the same way as in the case of Experimental Example 1. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 3.

TABLE 3 Number of Defectives in Impurity Components High Temperature Load Content ratio Life Test Sample (Parts by 1000 2000 Number Details Mol) hours hours 301 0.4Hf, 0.1Ag 0.50 0/100 0/100 302 0.25Sr, 0.02Zn 0.27 0/100 0/100 303 0.1Zr, 0.07Zr, 0.01Ag 0.18 0/100 0/100 304 0.5Zr, 0.05Ni, 0.1Zn 0.65 0/100 0/100 305 0.2Zr, 0.1Na 0.30 0/100 0/100 306 0.5Ni, 0.02Hf, 0.02Ag 0.54 0/100 0/100 307 0.4Pd, 0.01Zn, 0.03Na 0.44 0/100 0/100 308 5.0Ni 5.00 0/100 0/100 309 1.2Ag, 1.5Zr 4.30 0/100 0/100 310 1.8Ni, 0.1Zr 1.90 0/100 0/100

As can be seen from Table 3, for each of samples 301 to 310 containing impurities, no high temperature load life test detective was present not only after a lapse of 1000 hours but also after a lapse of 2000 hours, and the samples exhibited excellent reliability.

Experimental Example 4

Experimental Example 4 corresponds to Experimental Example 1, but the main component was (Ba,R)(Ti,Mn)O3 in Experimental Example 1, whereas the main component was (Ba,Ca,R)(Ti,Mn)O3 in Experimental Example 4.

(A) Production of Ceramic Raw Material

First, respective powders of fine BaCO3, CaCO3, Gd2O3, TiO2, and MnCO3 were prepared as starting materials for the main component, weighed to realize a (Ba0.55Ca0.01Gd0.01)(Ti0.995Mn0.005)O3 ceramic, and mixed with water as a medium in a ball mill for 8 hours. Then, evaporative drying was carried out, and calcination was carried out at a temperature of 1100° C. for 2 hours, thereby realizing a main component powder.

Next, respective powders of V2O5 and SiO2 to serve as accessory components were prepared, and weighed so that 0.25 parts by mol of V and 1.5 parts by mol of Si were present with respect to 100 parts by mol of the main component when blended with the main component powder, followed by mixing with water as a medium in a ball mill for 24 hours. Then, evaporative drying was carried out, thereby giving a dielectric ceramic raw material powder.

(B) Production of Laminated Ceramic Capacitor

To the ceramic raw material powder, a polyvinyl butyral based binder and ethanol were added, followed by mixing in a wet manner in a ball mill for 16 hours to produce a ceramic slurry. In this step of mixing in a wet manner in the ball mill for 16 hours, the balls used were changed to have diameters of 2 mm, 1.5 mm, 1 mm, 0.8 mm, 0.6 mm, 0.5 mm, and 0.3 mm, respectively, for samples 401, 402, 403, 404, 405, 406, and 407, thereby changing the “Ratio of Area of M region” in main component grains of the sintered dielectric ceramic obtained in a subsequent firing step, as shown in Table 4.

Then, the same steps as in the case of Experimental Example 1 were carried out to obtain laminated ceramic capacitors as samples.

(C) Structural Analysis and Characterization of Ceramic

For the laminated ceramic capacitors obtained, the “Ratio of Area of M region” was obtained in the same way as in the case of Experimental Example 1. The results are shown in Table 4.

In addition, a high temperature load life test was carried out in the same way as in the case of Experimental Example 1 for the laminated ceramic capacitors obtained. It is to be noted that the laminated ceramic capacitors were evaluated after a lapse of 3000 hours in addition to after a lapse of 1000 hours and after a lapse of 2000 hours in Experimental Example 4. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 4.

TABLE 4 Number of Defectives in High Sample Ratio of Area Temperature Load Life Test Number of M region 1000 hours 2000 hours 3000 hours 401 0 0/100 0/100 0/100 402 4 0/100 0/100 0/100 403 10 0/100 0/100 0/100 404 11 1/100 1/100 3/100 405 17 1/100 2/100 4/100 406 19 1/100 5/100 6/100 407 51 1/100 10/100  15/100 

As can be seen from Table 4, samples 401 to 403 had a “Ratio of Area of M region” of 10% or less, no detective was seen in the high temperature load life test, not only after a lapse of 1000 hours and after a lapse of 2000 hours but also after a lapse of 3000 hours.

On the other hand, samples 404 to 407 had a “Ratio of Area of M region” over 10%, and defective(s) were present after a lapse of 1000 hours in the high temperature load life test.

It is determined from these results that favorable reliability can be obtained when the main component is (Ba,Ca,R)(Ti,Mn)O3 and when the “Ratio of Area of M region” is 10% or less.

Experimental Example 5

In Experimental Example 5, a dielectric ceramic was evaluated containing (Ba,Ca,R)(Ti,Mn)O3 as a main component as in the case of Experimental Example 4 but having a varied Ca content, R content, and Mn content.

(A) Production of Ceramic Raw Material

A dielectric ceramic raw material powder was obtained in the same way as in the case of Experimental Example 4, expect that the composition of (Ba1−x−y/100Cax/100Hoy/100)(Ti1−z/100Mnz/100)O3 as a main component powder was adjusted so that the content x of Ca and content y of Ho as R at (Ba,Ca,R) sites, respectively, had values shown in the columns “x” and “y” in Table 5, and the content z of Mn at (Ti,Mn) sites had values shown in the column “z” in Table 5.

(B) Production of Laminated Ceramic Capacitor

The dielectric ceramic raw material powder was used to manufacture laminated ceramic capacitors in the same way as in the case of Experimental Example 4. It is to be noted that in the step of mixing in a wet manner in a ball mill, balls 1.5 mm in diameter were used to mix the powders for 16 hours, as in the case of sample 402 in Experimental Example 4.

(C) Structural Analysis and Characterization of Ceramic

The ceramic structure analysis carried out in the same way as in the case of Experimental Example 4 resulted in a “Ratio of Area of M region” of around 3.5% for any of samples 501 to 513.

In addition, the high temperature load life test was carried out in the same way as in the case of Experimental Example 4. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 5.

TABLE 5 Number of Defectives in High Temperature Load Life Test Sample 1000 2000 3000 Number x y z hours hours hours 501 1.00 1.50 0.50 0/100 0/100 0/100 502 4.30 0.20 0.70 0/100 0/100 0/100 503 7.90 1.90 0.64 0/100 0/100 0/100 504 0.01 0.70 0.90 0/100 0/100 0/100 505 15.0 0.90 0.70 0/100 0/100 0/100 506 17.0 1.90 0.50 0/100 0/100 1/100 507 2.10 0.01 0.21 0/100 0/100 0/100 508 1.50 2.00 0.35 0/100 0/100 0/100 509 3.40 2.20 0.55 0/100 0/100 2/100 510 5.90 1.50 0.01 0/100 0/100 0/100 511 14.1 0.70 1.00 0/100 0/100 0/100 512 0.60 0.60 1.10 0/100 0/100 2/100 513 16.5 2.40 1.30 0/100 1/100 3/100

As can be seen from Table 5, samples 501 to 505, 507, 508, 510 and 511 with a content “x” of Ca of 15 or less, a content “y” of Ho as R in the range of 0.01 to 2, and a content “z” of Mn in the range of 0.01 to 1.0, no detective was present in the high temperature load life test, not only after a lapse of 1000 hours but also after a lapse of 2000 hours and further after a lapse of 3000 hours.

On the other hand, sample 506 with a content “x” of Ca over 15, sample 509 with a content “y” of Ho as R outside the range of 0.01 to 2, and sample 512 with and content “z” of Mn outside the range of 0.01 to 1.0, had no defectives present after a lapse of 1000 hours or after a lapse of 2000 hours, but defective(s) were present after a lapse of 3000 hours in the high temperature load life test. In addition, sample 513 with a content “x” of Ca over 15, a content “y” of Ho as R outside the range of 0.01 to 2, and a content “z” of Mn outside the range of 0.01 to 1.0, had no defective were present after a lapse of 1000 hours, defective(s) were present after a lapse of 2000 hours and after a lapse of 3000 hours in the high temperature load life test.

It is determined from these results that higher reliability can be obtained when the Ca content “x” is 15 or less, when the R content “y” falls within the range of 0.01 to 2, and when the Mn content “z” falls within the range of 0.01 to 1.0.

Experimental Example 6

In Experimental Example 6, the influences of the impurities were evaluated while using (Ba,Ca,R)(Ti,Mn)O3 as a main component in the same way as in the case of Experimental Example 4. Experimental Example 6 corresponds to Experimental Example 3 described above.

(A) Production of Ceramic Raw Material

A dielectric ceramic raw material powder was obtained in the same way as in the case of Experimental Example 4, expect that impurity component amounts shown in Table 6 were added to 100 parts by mol of the dielectric ceramic raw material obtained in Experimental Example 4, so as to provide the content ratios shown in Table 6.

(B) Production of Laminated Ceramic Capacitor

The dielectric ceramic raw material powder was used to manufacture laminated ceramic capacitors in the same way as in the case of Experimental Example 4. It is to be noted that in the step of mixing in a wet manner in a ball mill, balls 1.5 mm in diameter were used to mix the powders for 16 hours, as in the case of sample 402 in Experimental Example 4.

(C) Structural Analysis and Characterization of Ceramic

The ceramic structure analysis carried out in the same way as in the case of Experimental Example 4 resulted in a “Ratio of Area of M region” of around 3.5% for any of samples 601 to 610.

In addition, the high temperature load life test was carried out in the same way as in the case of Experimental Example 4. The results are shown in the column of “Number of Defectives in High Temperature Load Life Test” in Table 6.

TABLE 6 Number of Defectives in High Temperature Impurity Components Load Life Test Sample Content ratio 1000 2000 3000 Number Details (Parts by Mol) hours hours hours 601 0.4Hf, 0.1Ag 0.50 0/100 0/100 0/100 602 0.25Sr, 0.02Zn 0.27 0/100 0/100 0/100 603 0.1Zr, 0.07Zr, 0.01Ag 0.18 0/100 0/100 0/100 604 0.5Zr, 0.05Ni, 0.1Zn 0.65 0/100 0/100 0/100 605 0.2Zr, 0.1Na 0.30 0/100 0/100 0/100 606 0.5Ni, 0.02Hf, 0.02Ag 0.54 0/100 0/100 0/100 607 0.4Pd, 0.01Zn, 0.03Na 0.44 0/100 0/100 0/100 608 5.0Ni 5.00 0/100 0/100 0/100 609 1.2Ag, 1.5Zr 4.30 0/100 0/100 0/100 610 1.8Ni, 0.1Zr 1.90 0/100 0/100 0/100

As can be seen from Table 6, no detective was present in the high temperature load life test for each of samples 601 to 610 containing impurities, not only after a lapse of 1000 hours but also after a lapse of 2000 hours and further after a lapse of 3000 hours, and the samples exhibited excellent reliability.

While Y, Dy, Gd, or Ho was used for an accessory component R whereas V was used as M for an accessory component in the experimental examples described above, it has been confirmed that substantially the same results are obtained even when La, Ce, Pr, Nd, Sm, Eu, Tb, Er, Tm, Yb, or Lu other than Y, Dy, Gd, or Ho is used as R or when Fe, Co, W, Cr, Mo, Cu, Al, or Mg other than V is used as M.

Claims

1. A dielectric ceramic comprising:

a main component which is (Ba1-a-bCabRa)(Ti1-cMnc) where a is 0.0001-0.02, b is 0-0.15, and c is 0.001-0.01,
in which R is at least one member selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; and
M and Si as accessory components in which M is at least one member selected from the group consisting of Fe, Co, V, W, Cr, Mo, Cu, Al, and Mg,
wherein the area of a region in which M is present is 10% or less on average on a cross section of each main component grain.

2. The dielectric ceramic according to claim 1, wherein the main component which is (Ba1-aRa)(Ti1-cMnc).

3. The dielectric ceramic according to claim 2, wherein R comprises Y or Dy.

4. The dielectric ceramic according to claim 1, wherein b is greater than 0.

5. The dielectric ceramic according to claim 4, wherein R comprises Y or Dy, and M comprises V.

6. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 5.

7. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 4.

8. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 3.

9. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 2.

10. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 1.

11. The dielectric ceramic according to claim 1, wherein R comprises Y or Dy.

12. A laminated ceramic capacitor comprising:

a capacitor main body comprising a plurality of stacked dielectric ceramic layers and a plurality of internal electrodes formed along interfaces between the dielectric ceramic layers; and
two external electrodes disposed at positions different from each other on an external surface of the capacitor main body and electrically connected to different ones of the internal electrodes,
wherein the dielectric ceramic layers are formed of the dielectric ceramic according to claim 11.
Patent History
Patent number: 8383536
Type: Grant
Filed: Jun 22, 2010
Date of Patent: Feb 26, 2013
Patent Publication Number: 20110019336
Assignee: Murata Manufacturing Co., Ltd. (Nagaokakyo-Shi, Kyoto-fu)
Inventors: Megumi Fukuda (Yasu), Takayuki Yao (Higashiomi)
Primary Examiner: Karl Group
Application Number: 12/820,414
Classifications
Current U.S. Class: And Trivalent Metal Oxide (501/139); Composition (361/321.4); And Divalent Metal Oxide Other Than Alkaline Earth Oxide Or Magnesium Oxide (501/138)
International Classification: C04B 35/468 (20060101); H01G 4/06 (20060101);